The present invention relates to an electric furnace of variable geometry for induction heating of metallic products, especially products of large volume, such as steel billets, which are upright placed into the interior of the furnace.
A furnace of this type is described in the French Pat. No. 2,339,316. In this furnace the heating means is constituted by a planar inductor with a sliding magnetic field, which constitutes an essential element of at least one large wall of the furnace which is laterally movable. This inductor comprises bar-shaped electric conductors located in slots provided in a face of the magnetic yoke which is directed toward the interior of the furnace and in the following designated as "active face of the inductor".
One of the absolutely necessary features of such a furnace is to assure the maintenance of the temperature of the inductor at an acceptable level, in view of the thermic charge resulting from the internal heating and from the radiation of the product in the furnace.
This thermic protection of the inductor is obtained in the mentioned patent by the combined action of a refractory covering provided on the active face of the inductor and a cooling fluid circulated in the aforementioned slots.
Such a solution has its drawbacks if one considers for example that, in the case of an inductor with a sliding field, the air gap plays an important role for the electric output of the furnace, and that for this reason the thickness of the refractory covering has to be as small as possible.
A corresponding observation relates to the cooling in the slots, especially when, in accordance with the construction described in the aforementioned patent, the electrical conductors are bars of the type "Roebel", designed to facilitate the passage of currents of necessary high intensity. In this case, the possibility of cooling by internal circulation of cooling fluids is much more limited than for tubular conductors which are used for the heating by solenoids or other types of inductors with a stationary magnetic field.
According to a preferred realization described in the above-mentioned patent, the thermic protection of the inductor is accomplished by a circulation of cooling fluid in channels parallel to the bars, placed in front of the slots. Here too, certain difficulties may arise, for instance the difficulties of a practical construction since it is not at all simple to place such channels in the slots of the yoke, further difficulties of a mechanical nature due to the vibration of the inductor during passage of an alternating current therethrough, and the additional difficulty of electric nature since the channels extending parallel to the conductive bars may become the seat of parasitic Foucault currents.